In existing wireless communication systems, a link adaptation technology including adaptive modulation coding (Adaptive Modulation Coding, AMC) and hybrid automatic repeat-request (Hybrid Automatic Repeat-reQuest, HARQ) is applied widely. Core concepts of the link adaptation technology is that the quality of a wireless link is rapidly adapted with the AMC technology to improve spectrum efficiency and throughput of the system, and that a data lose due to a burst error is further reduced in conjunction with HARQ technology to further improve a reliability of a transmission.
An efficient implementation of the link adaptation efficiently depends on an accuracy and efficiency of obtained link (or channel) status information. A process of obtaining channel status information (Channel Status Information, CSI) in the existing systems includes obtaining an uplink CSI and obtaining a downlink CSI. Specifically, the uplink channel status information is detected by a certain signal sent from a base station on a network side to a terminal; and the downlink channel status information is detected by a certain signal sent from the terminal to the base station on the network side and then the detected downlink channel status information is fed back to the network side.
Taking a downlink adaptation as an example, the terminal detects the downlink CSI in a preset period and feeds back the detected downlink CSI to the network side. Information fed back to the network side may include channel quality information (Channel Quality Information, CQI), a recommended precoding matrix indicator (Precoding Matrix Indicator, PMI), a recommended spatial multiplexing dimension (Rank Indication, RI) and the like. Specifically, the CQI is used by a schedule module for determining a resource allocation policy and selecting a modulation coding scheme (Modulation Coding Scheme, MCS), so as to determine an optimal MCS matching with a current quality of a channel. If a measured result of the CQI is large, i.e. the measured result is better than an actual channel quality, robustness (Robustness) of an employed MCS may decrease, which may result in an increased retransmission probability due to the loss of transmission data and a poor influence for effective throughput of the system. If the measured result of the CQI is small, i.e. the measured result is poorer than the actual channel quality, a rate is reduced unnecessarily and thus transmission efficiency and system throughput are reduced. Therefore, the measured result of the CQI is important for the system performance.
In existing wireless communication systems which take 3rd generation partnership project (3rd Generation Partnership Project, 3GPP) long term evolution (Long Term Evolution, LTE) system as a typical example, an application of multiple input multiple output (Multiple Input Multiple Output, MIMO) multi-antenna technology may affect the accuracy of a CQI feedback. Therefore, the measured CQI usually does not match with the actual CQI of the channel in the existing wireless communication systems. Specifically, an assumed transmission mode (Transmission Mode, TM) applied to feed back the CQI may differ from a TM applied to the transmutation of the base station, because multiple TMs are applied. For example, the TM applied to the transmutation of the based station is TM8, and the TM applied to feed back the CQI is TM2. Due to an introduction of multiple user (Multiple User, MU), a Single User (SU)-based feedback CQI cannot express the channel quality scheduled based on MU. After beamforming is applied, interference on an adjacent cell may be changed as a position of a service terminal is changed, thereby the CQI measured and fed back by a terminal in the adjacent cell can not trace an inter-cell interference, and the measured channel quality does not match with the actual channel quality.
In order to solve the issue that the measured CQI differs from the actual CQI of the channel, a scheme is provided in the existing technology, in which a CQI value is corrected with open loop link adaptation (Open Loop Link Adaptation, OLLA). Specifically, assuming that γ′ is a target corrected value of CQI SINR, then γ′=γ−offset, in which γ is a CQI value (represented by signal to interference plus noise ratio (SINR)) reported by user equipment (User Equipment, UE) and offset is a corrected value. The base station needs to adjust offset each time after receiving an acknowledgement or negative acknowledgement (ACK/NACK) message from the terminal. If the ACK message is received, then offset=offset−BLERtarget·Δ.
BLERtarget is an expected block error rate (Block Error Rate, BLER) of the UE, Δ is an adjusting step of offset. If the NACK message is received, then offset=offset+(1−BLERtarget)·Δ.
The essence of OLLA scheme is to correct an obtained incorrect CQI. It is attempted to improve the CQI value with a smaller step in the case of a good channel quality (the received ACK is used as a flag); and the UE reduces the level of MCS gradually as soon as possible in the case of a poor channel quality (the received NACK is used as a flag), and hence a success rate of a demodulation is improved.
The inventor found that the OLLA scheme according to the above existing technologies attempts to approach the actual CQI value by continuous iteration. However, the actual CQI value may be changed approach. Therefore, the accuracy of such approach scheme is not good and there still may be a large difference between the obtained CQI and the actual channel quality.